Preparation of aryl halides

ABSTRACT

The invention relates to a process for the preparation of an aryl dihalide by heating an aryldisulfonyl halide in the presence of an elemental halogen.

United States Patent Kirch Sept. 5, 1972 [54] PREPARATION OF ARYLHALIDES [56] References Cited [72] Inventor: Lawrence S. Kirch,Huntington OTHER PUBLICATIONS Valley, Pa. 19006 Morrison et al., OrganicChemistry, p. 35, (1959). 7 A R Allyr& Bacon, Inc., Boston, Mass. l 3].Sslgnee 22 li phla Miller et al., J.A.C.S., v01. 79, p. 4187-4191, 1957Filedl March 5, 1969 Primary Examiner-Lorraine A. Weinberger [21] Appl.No.: 804,677 Assistant Examiner-Richard D. Kelly Attorney-Carl A.Castellan and George W. F, Sim- [52] US. Cl; ..260/544 M, 260/651 R,260/651 F, mons 260/515 A, 260/476 R, 260/465 G ABSTRACT 51/58 Theinvention relates to a process for thepreparation of an aryl dihalide byheating an aryldisulfonyl halide in the presence of an elementalhalogen.

3 Claims, No Drawings ing elemental halogen an arylsulfonyl halidehaving the formula wherein R is a meta-directing, deactivatingsubstituent and X is chlorine or bromine.

By a meta-directing, deactivating substituent is meant any substituentwhich will deactivate a benzene ring towards electrophilic substitution,so that electrophilic substitution will take place preferentially atpositions meta to the substituent. Among the substituents which R canrepresent are nitro, cyano, formyl, carboxy, trichloromethyl,trifluoromethyl, quaternary ammonium, including trialkyl ammonium, andcarbalkoxy, such as carbomethoxy, carbethoxy, carbobutoxy, andcarbohexyloxy. The reaction proceeds smoothly, with evolution of sulfurdioxide, to give a high yield of the aryl halide. The reaction issubstantially completed when sulfur dioxide ceases to evolve from thereaction mixture.

The process of the invention may be carried out over a broad temperaturerange, and the temperature at which the reaction is run will depend inpart on the arylsulfonyl halide which is used as starting material.Furthermore, the temperature may be varied over the course of thereaction. In general, the reaction will be run within the temperaturerange of about 160 to 270 C.

A wide variety of arylsulfonyl halides can be reacted according to theprocess of the invention. Examples of arylsulfonyl halides which can bereacted according to the process of the invention include3,5-dichlorosulfonylbenzoyl chloride, 3,5-dibromosulfonylbenzoylbromide, 3,5-dichlorosulfonylbenzoic acid, ethyl 3,5-dichlorosulfonylbenzoate, 3,5-dichlorosulfonylbenzonitrile,3,5-dichlorosulfonylaniline hydrochloride, 3 ,5-dichlorosulfonyl-N,N,N-trimethylanilinium chloride, 3,5-dichlorosulfonylbenzaldehyde,3,5-dichlorosulfonylnitrobenzene, and3,5-dichlorosulfonylbenzotrichloride.

An aryl halide which is produced by the process of the invention can beseparated from the reaction mixture by any convenient means. Generally,the aryl halide is advantageously removed from the reaction mixture bydistillation at reduced pressure.

In general, no solvent need be used in carrying out the process of thereaction. When no solvent is used, the temperature at which the reactionis carried out will be higher than the melting point of the arylsulfonylhalide starting material. However, a solvent which is inert to thereaction process can be employed. Among the solvents which areespecially suitable are those aromatic hydrocarbons, ethers, nitriles,and carbalkoxy compounds which are highly halogenated, that is, in

which most of the hydrogen atoms of the parent com- 7 pound have beenreplaced by halogen atoms. Preferably, the solvent will have a higherboiling point than the aryl halide product so that the product can beconveniently removed by distillation.

An essential feature of the process of the invention is the presence inthe reaction system of an elemental halogen, which acts as a catalyst inthe reaction. Since the halogen is employed as a catalyst, the quantitywhich is used can vary over a wide range and any amount which willproduce the desired catalysis can be used. Advantageously, the halogenis passed through the system at a steady flow rate, this flow rate beingdetermined by the reaction temperature, the arylsulfonyl halide beingreacted, and other factors. Generally, about 0.01 to about 1 mole of thehalogen are passed into the system for each mole of arylsulfonyl halidewhich is reacted. The preferred range is about 0.1 to 0.5 mole ofhalogen per mole of arylsulfonyl halide.

The reaction time will depend on the reaction temperature, thearylsulfonyl halide which is reacted, and other factors. In general, areaction time of about 1 to 20 hours will be sufficient to complete thereaction.

The process of the reaction has many advantages in the preparation ofaryl halides. It is a very clean reaction, giving a high yield of thedesired product with little formation of undesired or undesirable sideproducts, and leaving very little residue on distillation. Furthermore,by means of this process, many 3,5-dihalo benzene compounds, thepreparation of which formerly necessitated involved procedures, can nowbe prepared simply. For example, since direct chlorination of benzoylchloride gives mainly the 3,4- and 2,3- isomers, the preparation of3,5-dichlorobenzoyl chloride formerly required a complicated six-stepprocedure with relatively low overall yield. By utilizing the process ofthe present invention, 3,5- dichlorobenzoyl chloride can be prepared ina fourstep, one-pot procedure (i.e., without isolating any of theintermediates), with very high overall yield.

The arylsulfonyl halides which are used as starting materials in theprocess of the invention can be prepared by any of the methods wellknown to those skilled in the art. One preparation which can beadvantageously employed comprises the steps of sulfonation of thearomatic compound with sulfur trioxide or oleum, followed by conversionof the sulfonic acid thus formed to the sulfonyl halide with aphosphorus oxyhalide, a phosphorus pentahalide or similar reagent.

The following examples will further illustrate this invention but arenot intended to limit it in any way.

EXAMPLE 1 Desulfoxylation of 3,5-Dichlorosulfonylbenzoyl ChlorideEighty-nine g. (0.264 mole) 3,5-dichlorosulfonyl benzoyl chloride ischarged to a distilling flask fitted with a gas inlet tube, thermometerand condenser and slowly heated to 210 C. The melt is maintained at 210C. while a stream of chlorine (0.25 g./min.) is in troduced below thesurface of the melt. Upon introducing the chlorine, evolution of sulfurdioxide is noted. The S0 evolution lasts for 2 hours. The chlorine isthen terminated and the batch cooled. The resulting crude produce isvery pale yellow andv weighs 54 g. Straight lead distillation affords 52g. (94 percent yield) of 3,5-dichlorobenzoyl chloride (b. 60+67/ C./0.3mm. Hg) which is 100 percent pure by GLC.

EXAMPLE 2 Preparation of 3,5-Dichlorobenzoyl Chloride from Benzoic AcidOne hundred and twenty-two g. (1 mole) of benzoic acid is charged to aflask fitted with a thermometer, stirrer, condenser, gas inlet tube anddropping funnel. The benzoic acid is heated to 125 C. and then 176 g.(2.2 moles) 80;, are added over a period of 2 hours. During theaddition, the temperature is gradually increased to 170 C. After all theS has been added, the batch is heated to 220 C. and maintained at thistemperature for 16 hours. The batch temperature is gradually reduced to120 C. whileadding 460 g. (3 moles) POCl The batch is maintained at 120C. for an additional hour and then 151 g. (1.1 moles) PC13 and 85 g.(1.2 moles) Cl gas are simultaneously introduced over a period of 1hour. During this addition and for l more hour, the temperature ismaintained at 120 C.

The condenser is then replaced with a straight lead distillation headand POCl distilled from the mix at atmospheric pressure. Four-hundred g.(87 percent) P0Cl suitable for recycle, is recovered. After the POCl hasbeen distilled, the batch is heated to 220 C.

and Cl, gas is introduced below the liquid surface at a rate of 0.25g./min. SO, evolutionstarts at once and continues for about 4 hours. Thebatch is then cooled to 50 C. and 3,5-dichlorobenzoyl chloride distilledfrom the crude mix. The product cut weighs 168 g. and contains 91percent 3,5-dichlorobenzoyl chloride (73 percent yield) and 3 percentm-chlorobenzoyl chloride (3 percent yield based on benzoic acid).

It is to be understood that changes and variations may be made withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

I claim:

1. A process for preparing 3,5-dichlorobenzoyl chloride, which comprisesheating 3,5-dichlorosulfonylbenzoyl chloride to its melting point,passing chlorine into the molten mass, and maintaining the mass inmolten condition until evolution of sulfur dioxide ceases.

2. A process for preparing 3,5-dichlorobenzoyl chloride which comprisesheating 3,5-dichlorosulfonylbenzoyl chloride at a temperature of aboutC. to about 270 C. in the presence of chlorine with the evolution ofsulfur dioxide gas.

3. A process according to claim 2 wherein said heating is maintaineduntil the evolution of sulfur dioxide substantially ceases.

2. A process for preparing 3,5-dichlorobenzoyl chloride which comprisesheating 3,5-dichlorosulfonylbenzoyl chloride at a temperature of about160* C. to about 270* C. in the presence of chlorine with the evolutionof sulfur dioxide gas.
 3. A process according to claim 2 wherein saidheating is maintained until the evolution of sulfur dioxidesubstantially ceases.